DE-OS No. 1477040 discloses a tool holder for holding tools for processing rotating work pieces comprised essentially of two opposed wheels or rollers between which a work piece can be processed. The tool holder disclosed in this publication is provided with separation rollers and is forced radially into a tubular work piece by means of a support. The tangential feed of the rollers results in the penetration of the material of the tube. In order to ensure a complete separation, the clear distance between the separation rollers must be smaller than the inner diameter of the tube. Conventional cutting rollers are employed for the separation of the tube, so that, especially at the end of the separation process, it is possible for small portions of the material to be radially displaced over the inner surface of the tube. The smaller this edge is, the less subsequent machining is necessary or the less material waste must be taken into account. The cutting edges of the cutting roller wear relatively rapidly, however, so that a tool replacement is necessary after a short period of time. In deforming rollers (i.e., rollers that effect displacement of the material by deformation rather than cutting) are employed instead of the cutting rollers, for example, with rounded profiles which are thereby less subject to wear, the remaining turned-back edges are larger and thereby the expense required by the necessity of further machining is increased.
The combination of cutting rollers and deforming rollers has been proposed for the solution to this problem in EPA No. 0013832. The deforming tool 40 forms a groove in which cutting roller 12 is subsequently inserted. In this arrangement the cutting roller is forced in a conventional manner into the material, the radial forces imposed by the cutting roller being opposed on the diametrically opposite side of the tube by a back-up roller (FIG. 7). The displacement roller forms a V-shaped groove or separating line which is less sharp than the edge of the cutting roller and thereby decreases the side friction of the cutting roller. The cutting roller must nevertheless perform the entire separation work, so that the wear of the cutting edge cannot consequently be minimized.